This invention relates to pharmaceutical tablet press mechanisms, and more particularly, relates to a control and monitoring system for operation of a high speed rotary tablet press.
Rotary tablet press mechanisms designed to compress and form medicinal or related powders or granules into tablets have long been known in the pharmaceutical art. An example of prior art tablet presses is disclosed in U.S. Pat. No. 3,255,716 issued June 14, 1966. In such rotary presses, powders or other materials that can be formed into tablets are placed in one of a plurality of generally cylindrical dies mounted within a rotary die holding turret. A pair of opposed cam operated punches compress the powder from both ends of each tablet forming die and thereby compact the powder into an individual tablet. The rotary turret arrangements allows a plurality of punch and die sets to continuously produce tablets around the circular path followed by the rotary press by sequentially contacting a arrangement of cam above and below the turret that lift and lower the punches. In modern tablet press machines, pharmaceutical tablets are produced at rates as high as 12,000 tablets per minute.
It is highly desirable that all tablets prepared by rotary tablet press mechanisms be of uniform and precisely controlled size and weight. This is especially true for medicinal tablets, as carefully prescribed dosage amounts are difficult to achieve without accurate tablet size and weight control Inaccuracies in tablet size and weight stem from a variety of different circumstances, but most commonly result from uneven introduction of the powders into the die and punch combinations. Inaccuracies can also result from imperfections or wear in the tablet press or die elements, or from changes in the density or moisture content of the compressed powder.
Several prior art mechanisms have been employed to evaluate the weight of compressed tablets and determine if such tablets are defective. Generally, individual tablets are monitored by evaluating the compression between the punches during tablet formation. Overweight tablets, resulting from excessive powder or granular material placed between the opposing punches, will cause higher than normal compacting forces. Likewise, underweight tablets, resulting from a smaller than normal quantity of powder or granular material between the opposing punches, will result in less than normal compressive forces between the opposing punches. Thus over and underweight tablets are typically detected in tablet presses through use of a strain gauge (or related mechanism) for measuring the forces in the opposing punches. Such a strain gauge is disclosed in U.S. Pat. No. 3,791,205 issued on Feb. 12, 1974. U.S. Pat. No. 3,734,663, issued May 22, 1973, discloses a control circuitry that monitors, and if necessary, changes the amount of powder placed in the die in response to measured tablet compressive forces, as detected by changes in resistance in a strain gauge.
Tablet press mechanisms also typically include a structure for removing the formed tablet from the punches and dies. Normally, rotary tablet press mechanisms include a second cam system that causes the lower punches to lift the formed tablet, after compression, to the surface of the rotating turret. A blade or the like is then disposed slightly above the rotary disc at a location intersecting the path of the dies and hence the tablets that have been lifted from the dies. Contact of the tablet with the blade then scrapes the tablets from the turret to a discharge shoot.
Often, blade mechanisms of the kind described above are combined with a reject gate, such as is disclosed in U.S. patent application Ser. No. 650,346 filed Sept. 13, 1984, and owned by the same entity as the present application. Defective tablets are detected through analysis of the punch forces as established by the strain gauge, and a pneumatic air jet is timed to deflect defective tablets away from the blade into a reject chute. Proper operation of such a mechanism requires instrumentation for precise control of the pneumatic air jet in response to a signal indicating a defective tablet. Such instrumentation in turn requires highly precise devices to produce the signal indicating the specific defective tablet to be rejected. For very high speed mechanisms, such as those producing as much as 12,000 tablets per minute, even minor imprecisions can result in rejection of other than the specific defective tablet. To avoid such failures, tablet press control mechanisms are usually set to reject plurality of tablets in the vicinity of the detected defective tablet.
Additionally, unnecessary tablet rejection can be minimized if precise information regarding individual punch compression activity can be evaluated by an operator with a number of indicia displayed. Thus, when an operator is able to monitor compression forces precisely during the operation of the rotary press, and receives such further information as the range of compressing force produced by each punch set and statistical comparisons of the forces produced over time during press operation, mechanical and component wear problems can be identified while still incipient, and can thereafter be corrected before the problem is exacerbated. Likewise, individual mechanical variations between punches or cams can be detected, and adjustments made to compensate for differing die and punch wear or differing adjustment of other individual press components.
Many rotary press tablet machines that require monitoring are double acting presses, that is, the machine possesses a set of compressive cams on opposite sides of the turret that act simultaneously to produce tablets. For such double rotary tablet presses, a dual system of compression detectors, monitors, reject gates, and control systems is highly advantageous. Such dual monitoring allows comparison of the operation of each side of the tablet press during operation, so that to the extent possible, the operator can maintain equal efficiency of each side.
Accordingly, it is an object of this invention to provide a pharmaceutical tablet press control mechanism suitable for use with a double rotary tablet press that precisely monitors both tablet compression information and defective tablet rejection information.
It is a further object of this invention to provide such a press that monitors compression force for each individual punch set.
It is an additional object of this invention to provide such a press control and monitoring mechanism that provides information to an operator regarding press compression concurrent with operation of the system.
Another object of this invention is to provide such a tablet press control and monitoring system that produces a statistical abstract of press compression information.
Yet another object of this invention is to provide such a tablet press control and monitoring system that produces detailed information regarding tablet press performance concurrent with press operation in a manner that is both visually descriptive and relatively easy to use.